Why do you find that the blood of fish is red when you watch Kill Fish?

Let's talk about what fish is: fish has been with human beings for more than 5,000 years, and has formed an indissoluble bond with human beings, becoming an extremely important food and ornamental pet in human daily life. But what animal is a "fish"? Few people know how to define fish. With the development of science, people's definition of fish has changed a lot. Nearly 500 million years ago, the life course on the earth took a great leap, and the earliest fish-shaped animals appeared, which opened the prelude to the history of vertebrates, thus leading to the development of the animal kingdom and entering a new historical stage. Real fish first appeared more than 300 million years ago. Throughout the long history, a large number of fish have survived, and with the passage of time, they have long been extinct. Fish that live on the earth today are only a tiny part of the species that later appeared and evolved.

Humans can identify species and name them long ago. Generally speaking, "fish" includes all animals in the water, so many animals living in the water are named fish. Whales, seals, monitor lizards (giant salamanders), squid, octopus, starfish, sea squirrels, sponges and amphioxus are all confused with fish. What aquatic animals are the real "fish"? Different generations have different definitions of "fish". Two thousand years ago, the ancient Greek philosopher Plato (427-347 BC) defined fish as: "This kind of fish is made up of completely ignorant things. The master of transfiguration thinks that it is no longer worthwhile to give pure breath, because they are descendants of all kinds of evil and have unclean hearts. The shapeshifter threw them into the water and let them breathe the beautiful and pure air through the deep mud. This is the fish and oysters and all other aquatic animals, which are separated from each other as a punishment for the great folly. " Plato's views are full of creationism. Due to the development of modern science, this view has long been completely denied.

Erya, written by China in the early Han Dynasty, divided animals into four categories: insects, fish, birds and beasts. Among them, fish include lower vertebrates such as fish, amphibians and reptiles, as well as whales, shrimps, crabs and shellfish. /kloc-in the 8th century, the Swedish naturalist Linnaeus (1707— 1778) founded modern taxonomy. In his book, 1859, British biologist Darwin published The Origin of Species, which gave birth to systematic taxonomy. Since then, the definition and scope of fish have been determined. Which animals belong to "fish"? Modern taxonomists define "fish" as vertebrates that live in water all their lives, breathe through gills and swim with fins. Fish include three categories, namely oviduct fish, cartilaginous fish and bony fish. There are about 26,000 known fish species in the world, which is the largest group of vertebrates, accounting for 48. 1% of the total number of vertebrates. Most of them live in the ocean, and there are about 8600 species of freshwater fish. There are nearly 3,000 species of fish in China, among which about 1000 species are freshwater fish.

In the coarse sand in China's coastal shallow waters, there is a small "fish" with a slender body, a body length of less than 50 mm, and a sharp and translucent shape. Its scientific name is "amphioxus". Although it is a fish in shape, it is not a fish. Although amphioxus has a spinal cord on its back, it has no spinal structure, no bones, no obvious head and no heart. Amphioxus, similar to fish, is characterized by notochord, neural tube and branchial fissure, and belongs to the intermediate transitional group between invertebrates and vertebrates in taxonomy-protochordata, also known as Decapoda.

First, spring heating and upstream fish schools Jiangnan has been a land of fish and rice since ancient times. In Hengxingzhou area, hot-water grass fertilizer is suitable for fish reproduction and growth, so fishermen's fishing is the peak season all year round. 1950 or so. In spring and summer, big carp, silver carp and white striped fish can be seen jumping out of the water every three to five minutes, one after another, and the scales are golden yellow under the sunlight. Diving fish often fall into small wooden boats, and fishermen can eat for nothing. This big diving fish can weigh more than ten kilograms. Fishermen said it was because there were river pigs and baiji chasing food underwater, and the fish suddenly got scared and jumped out of the water. Before and after Tomb-Sweeping Day, the weather was fine, and groups of herring came from the upper reaches of the Yangtze River and slowly floated on the water along the coast. The area of a group of big fish is more than one acre (about 600 square meters). Fish swim around, the river ripples, like the wind blowing water, a vast expanse. Flocks of fish swim upstream and are easily caught in the net. Fishermen use floating nets to catch herring. When there are many fish, you can catch 100 kilograms a day. Herring meat is tender, delicious and nutritious, and one kilogram can be called more than 20. In spring, there are swordfish, puffer fish, shad and herring in the upper reaches. The most precious thing is pushing shad, which is a first-class famous dish at a senior banquet and tastes particularly delicious. The fishing period is no more than 60 days from Tomb-Sweeping Day to Mang Seed Festival. Su Dongpo wrote a famous poem when he was watching fish by the river in the Song Dynasty: Peach blossoms are three Liang outside the bamboo, and the duck prophet warms the river. The beach is covered with wormwood, asparagus is beginning to sprout, and puffer fish are preparing to swim upstream from the sea back to the river. The poetry in the works of the CPSU is spring water heating and peach blossoms in full bloom. Jiangzhou beach is full of a wormwood seedling; Upstream of the fish, there is a spring. From the Northern Song Dynasty to 1950 years ago, the ecological environment in the middle and lower reaches of the Yangtze River has not changed much for thousands of years. In the old days, there was a fish queen mother temple in Xiaogushan, Jiangxi Province, which was praised by several generations of fishermen. Every spring, all kinds of fish go to Chao Wang. In fact, this fish swims upstream to Chaohu, Poyang, Dongting and other great lakes to lay eggs and reproduce.

2. Quarry Fishing Village Because there are so many local fish, there are a group of resident fishermen in Xiaojiajiang, Hengxingzhou, who have been fishing here for generations, with a population of about 400 to 500, called' Flower Basket Collection'. Before liberation, a fishing village fort was built and one was chosen to be under the jurisdiction of the quarrying area. After liberation, a fishery society was established, which is now the Quarrying Fishery Brigade. Among the fishermen, Yuan and Wang are the majority. They catch swordfish, shad and puffer fish in spring; Fishing herring, white fish and carp in summer; Catch eels and crabs in autumn; Roll the net in winter and catch carp and silver carp. Whenever there is a north wind around the start of the autumn festival, fishermen will set up their nets and ride the wind and waves to catch eels in the main channel of the Yangtze River. Because the wind and waves are high, the eel floats on the river, which is very easy to catch, and it can catch three or four hundred kilograms a day for a long time. A big eel weighs two or three pounds, but fishermen who catch eels should be bold and cautious, and their shipbuilding skills are extremely high, otherwise there is a danger of capsizing. Around the Double Ninth Festival, it is the peak season for catching crabs. Fishermen are used to dropping crab nets from the middle of Muqiao River in Hexian County, sinking into the bottom of the river with trawls, and dragging them downstream from the main channel to the mouth of Cihu River to collect the nets. One net can catch 100 kilograms of crabs. Due to the high fishery output, these fishermen live a relatively affluent life. In the old days, fishermen were superstitious about river gods and water gods. Every boat was equipped with several wooden statues, and they burned incense and kowtowed in the morning and evening. During the Spring Festival, it is very lively to sacrifice pig heads, burn incense and set off firecrackers to Jiang Shen. When I was a teenager, I saw with my own eyes that the biggest carp caught by a steel hook boat weighed 62 Jin. 1950 In the spring, dangtu county held a small-scale agricultural exhibition in the quarry primary school, and fisherman Yuan Mou just caught a harpsichord weighing more than 280 kilograms. This fish has no scales, its whole body is blue and black, its mouth is as long as a sword, and its body is more than two meters long. It is a rare species in the Yangtze River and has been carried to the Development Hall for seven days. According to fishermen, this fish is over 100 years old.

Baiji dolphins chase fishermen who cast nets to fish in the water and birds in the mountains, rest at high tide and fish at low tide. At the high tide, all the fish swam into the river, and there were few fish in the shallow water on the shore. The Yangtze River is divided into two tides, day and night, and the tides turn with the moon. The first and fifteenth days of the first lunar month are meridian tides, that is, noon tides, the tenth and twentieth days are morning and evening tides, and so on. This is an eternal law of nature. Around beginning of spring, the temperature gradually became warmer, and baiji began to fish in the deep water of the main channel of the Yangtze River. A large number of deep-water fish rushed to the shallow water of the river beach. At this time, the fishermen cast a net and there were fish in the net. High yield and bumper harvest. In winter, in the depths of the river, there are pits washed by water at the bottom of the river, which are forty or fifty meters deep. Fish like to live in groups in pits, which are warm and safe. These deep puddles and sinks are called "fish nests". Before and after beginning of spring, it was sunny and sunny, and the net-casting boat was moored by the river. In the middle of the night, on the calm river, as long as you hear the exhalation of the white pomfret dolphin, it is chasing fish. All the fish swim to the shallow water of the river beach, and the fishermen have a bumper harvest. Sometimes, they can catch 100 kilograms in two hours, and the fishing time can last for a week. After that, the fish dispersed.

Badougou catches crabs, and the waves behind the Yangtze River push the waves ahead. There is a canal called Badougou in front of the author's house, which is the main waterway for discharging mountain torrents in Hengxingzhou. In the forties and fifties, there was no beach outside the dike and the river was deep. In winter, a century-old wooden boat can be moored on the shore. In the spring rain season, mountain torrents are discharged into the Yangtze River along the canal, and the fish in the middle reaches swim upstream into Badougou, and the fish in the lower reaches are caught with nets, which can catch dozens of kilograms at a time. Each silver carp weighs more than ten kilograms. Sometimes clods are used to throw fish into the water in the middle and upper reaches of the canal, and carp jump to the shore in horror. It can be seen that there are many fish in the canal. After beginning of autumn, the river began to ebb, and Baduangou opened the floodgates to release water. At this time, the chrysanthemum crabs were plump. After dusk, big crabs are crawling to the shore in the area around the sluice. The children nearby gathered at the water's edge, waiting to catch crabs. Dozens of big crabs can be caught every night. When I was a teenager, I caught crabs at most once. I caught more than 100 fat crabs overnight, each weighing half a catty. There is also a unique way for mainlanders to catch prawns in the river, that is, the net mouth is facing down and the prawns catch prawns against the water. At first, people on the mainland didn't know how to catch shrimp in this way. Once, a village woman was washing clothes by the river. It happened that a river shrimp stuck to her clothes, and the village woman dragged the prawn out of the water with her clothes. Inspired by this, people in continental Europe use a small fishing net to catch shrimp. The net mouth faces downstream, and the shrimp swim against the current. When they catch the net in the water, they will hold on to it. After three or five minutes, they can catch a dozen shrimps in one net, and they can catch two or three pounds of shrimps in one hour. Later, several continents made a living by catching shrimps in this way and became a profession. Fishing by the river in spring and summer is also very interesting. Fishing tackle is very simple. Tie the rolling ditch with hemp rope and put earthworms as bait to catch eels and silver whiskers. You can catch more than ten catties in one morning. The beard of silver carp weighs two or three Jin.

Before 1960, the river surface and river water in Hengxingzhou area have not been greatly polluted, and the villagers on the shore all drink river water, with a slight decrease in fish and shrimp; After the 1960s, a large amount of industrial wastewater was discharged into the Yangtze River without any treatment, and the river water pollution became more and more serious. Fish and shrimp caught along the river in Xuejiawa area are fresh, but they smell of sewage tar, so they are often inedible after being cooked. In the middle and lower reaches of the Yangtze River, more factories and domestic sewage are discharged into the Yangtze River, the water quality is getting worse year by year, and the fish in the river are decreasing day by day. After three years of natural disasters (1959- 196 1), the country has made great efforts to produce grain, and a large area of lakes has been opened for reclamation, and the water surface for fish farming has become less and less; Later, the number of motorboats in the river increased year by year, and a large amount of waste oil was discharged. Therefore, the ecological environment of the Yangtze River is getting worse and worse, and valuable fishery products are becoming scarcer and scarcer. After 1990, rare fish species such as shad, puffer fish, eel, swordfish and crab in the middle reaches of the Yangtze River were difficult to catch, while river pigs and baiji dolphins also disappeared one after another, and river fish suffered extinction. Due to the decrease in fish production, the fishing team had to find another way to make a living. Some of them run for transportation, and some enter the factory. Most fishermen went ashore, built houses and settled in the old archway of quarrying, and started some small factories to make a living. There are still a few fishermen who can't leave the water and still catch a small amount of fish and shrimp in the river to make a living. As described at the beginning of the Romance of the Three Kingdoms, "a fisherman with white hair is used to watching the spring breeze on the river". In recent years, although the national environmental protection department has made every effort to control it, it is impossible to return to the appearance of the 1940s and 1950s, or even gone forever. People of insight now think endangered species are precious. Similarly, the "river sentiment and fish interest" in the disappearing Yangtze River should be the same. In those days, the fisherman sang late and the sunset returned to the sails, but now the younger generation can't see it. Although writing this essay is the author's lyrical nostalgia for the past, it can leave behind the rich fish production and fishermen's customs in the Yangtze River between the lines for future generations to read and appreciate.

They inhabit almost all aquatic environments on earth-from freshwater lakes and rivers to saltwater oceans.

The earliest fish was a round-billed jawless fish that appeared on the earth during the Cambrian period 450 million years ago. Fish are easy to distinguish from each other in appearance. They constitute the largest group of vertebrates: there are 22,000 species of fish among 50,000 species of vertebrates.

Not all animals that live in water are fish. For example, whales are mammals. However, all fish can adapt well to life in water. They move with their fins. Fish has two pairs of fins-pectoral fin and ventral fin, which are located in two parts of the body; There is also a tail fin, which grows at the tail; And depending on the species, there are one or two dorsal fins on the back and a gluteal fin on the buttocks. They have a bladder filled with gas, called swim bladder, which enables the fish to sink, float and keep their position in the water. Only rays and sharks do not have this organ. Fish also have gills for breathing, and most kinds of gills are covered by gill cover bones. Cheeks are located on both sides of the head and behind the mouth. They are used to filter the water swallowed from the mouth, get oxygen from the water, and then discharge the water from an opening called branchial fissure. The size of different kinds of fish varies greatly. Their bodies consist of three parts: head, trunk and tail. The skin is covered with scales of different sizes and numbers. There is an obvious line on each side called lateral line, which is a sensory organ and is used to determine the direction. The muscles of some teleost fish are separated by some tiny bones.

The first fish that appeared on the earth had a round jawless mouth, and now only 70 kinds of such fish exist, forming jawless fish. Among these fish, lamprey is the most famous. They have no scales, thin and round, much like eels. Lamprey attaches itself to other fish through its mouth with sucker, and feeds on the blood of its host. Other fish are divided into two categories: bony fish and cartilaginous fish.

A bony fish has a pair of bones. There are primitive bony fish in this fish, and only some bones are hard bones. For example, fish of the suborder Holoptera (including Echinodermata), lungfish and sturgeon (such as sturgeon) are different from the more evolved teleost in that the bones of teleost are completely composed of hard bones. As representatives of bony fishes, sea eel, sole and stickleback have different shapes, but they all have extremely symmetrical tail fins and are covered with tiny scales (with a few exceptions, including eels and some carp). Bony fish are divided into several types. Eels are some fish, and their larvae look very different from adults. Herring is a group of fish. Carp contains almost all freshwater fish. Perch and tuna are fish whose tail fins are supported by hard spokes. They are called "spiny fins" and constitute the largest bony fish.

The skeleton of cartilaginous fish is completely composed of cartilage and strengthened by calcium. This kind of fish is mainly sharks and rays.

Eel is a small fish with a flat body at birth and is called "Little Eel". When they are mature, they have long, smooth bodies, usually without scales, and continuous fins along their backs. Eels live in rivers and lakes in Europe and America. They migrate to the algae sea in the northeast of the West Indies in the North Atlantic, where they breed. They die after their cubs are born. On the way back across the Atlantic, the young eels showed their adult form, and on the way back, they also began to breed in the sargasso sea.

Herring lives in the North Sea, the English Channel and the Baltic Sea. Adult fish have a pale abdomen and a dark blue or nearly black back. Like sardines and herrings, they live in groups, sometimes thousands of fish live together. For every fish, this is an effective self-defense method, because for a predator, only one target can be selected among many fish. When attacked, the fish disappeared almost immediately.

There are thousands of kinds of carp, almost all over the world. These freshwater fish have large scales, and their teeth are not fixed on their chins, but on their throats. Their mouths can move forward to suck food. Many species of Cyprinidae mainly live in calm rivers, small ponds and lakes in Asia and Europe, and their shapes and colors vary greatly. Some species have only a few large scales (mirror carp) or almost no scales (grass carp). These fish breed easily, and breeders have created many varieties. Carp mainly feed on plants and invertebrates. The spawning season depends on the water temperature, not too cold (at least 20℃). Female fish lay hundreds of eggs, but most young fish become food for other fish and even adult carp at birth.

Spiny fins appeared about 60 million years ago. Perch is a typical representative of this kind of fish. Their fins are supported by hard and sharp spokes, and there are thorns on their huge tail fins. Perch lives in lakes and rivers in Europe and North America. They eat invertebrates and small fish, including their own young fish. Other species of these fish live in the ocean, such as tuna and swordfish. They are powerful swimmers and can swim 100 kilometers per hour. Tuna can weigh up to 500 kilograms and is a carnivore. In fish, they have a unique ability to keep their body temperature higher than the water temperature. Their species include Pacific albacore tuna and Mediterranean and Atlantic bluefin tuna.

Sharks and rays are the main representatives of modern cartilaginous fish, which may have appeared 465.438 billion years ago. As the name implies, their bones are made of cartilage. Cartilage is a flexible material, which will harden after calcium supplementation and be solid like bone. Chondroid fish thrive in temperate and tropical seas. They breathe through their gills in the water. Gills communicate directly with the outside world through several gill slits behind the head. There are about 550 species of cartilaginous fish, of which 370 species are sharks, and the others are basically composed of rays and rays.

Fish is a lower vertebrate. It lives in water all its life, and there are fish in almost all waters in the world. Fish use gills to absorb oxygen from water, and use fins to make their bodies move and keep balance. Most fish also have swim bladders, which can be used to control the ups and downs of the body. Basic characteristics of fish: fish is a vertebrate; Fish generally have a streamlined body; It flows in the water by its tail and fins, and breathes by its cheeks. Fish living in different environments have different bodies: fish living near coral reefs are generally narrow; The fish living on the bottom of the sea looks like a flat thing. There are more than 20,000 species of fish in the world, which are widely distributed in rivers and lakes, among which the most species are fish living in the ocean. Some fish live in underground, mud and other special environments, and a few kinds of fish can survive for a period of time without water. There are more than 3,000 species in China. Fish is rich in protein, fat and other nutrients, except for a few poisonous fish (such as puffer fish). Fish scales, bones, fins and internal organs can all be comprehensively utilized by human beings.

I hope this information can help you.